Fatigue resistance of all-ceramic fixed partial dentures - Fatigue tests and finite element analysis.

OBJECTIVE: To estimate the fatigue resistance of a new translucent zirconia material in comparison to lithium disilicate for 3-unit fixed partial dentures (FPDs). METHODS: Eighteen 3-unit FPDs (replacement of first upper molar) with a connector size of 4mm×4mm were dry milled with a five-axis milling machine (Zenotec Select, Wieland, Germany) using discs made of a new translucent zirconia material (IPS e.max ZirCAD MT, Ivoclar Vivadent). Another 9 FPDs with a reduced connector size (3mm×4mm) were milled. The zirconia FPDs were sintered at 1500°C. For a comparison, 9 FPDs were made of IPS e.max Press, using the same dimensions. These IPS e.max Press FPDs were ground from a wax disc (Wieland), invested and pressed at 920°C. All FPDs were glazed twice. The FPDs were adhesively luted to PMMA dies with Multilink Automix. Dynamic cyclic loading was carried out on the molar pontic using Dyna-Mess testing machines (Stolberg, Germany) with 2×106 cycles at 2Hz in water (37°C). Two specimens per group and load were subjected to decreasing load levels (at least 4) until the two specimens no longer showed any failures. Another third specimen was subjected to this load to confirm the result. All the specimens were evaluated under a stereo microscope (20× magnification). The number of cycles reached before observing a failure, and their dependence on the load and on the material, were modeled, using a Weibull model. This made it possible to estimate the fatigue resistance as the maximum load for which one would observe less than 1% failure after 2×106 cycles. In addition to the experimental study, Finite Element Modeling (FEM) simulations were conducted to predict the force to failure for IPS e.max ZirCAD MT and IPS e.max Press with a reduced cross-section of the connectors. RESULTS: The failure mode of the zirconia FPDs was mostly the fracture of the distal connector, whereas the failure mode of the lithium disilicate FPDs observed to be the fracture of the connectors or multiple cracks of the pontic. The fatigue resistance with 1% fracture probability was estimated to be 488N for the IPS e.max ZirCAD MT FPDs (453N for repeated test), 365N for IPS e.max ZirCAD MT FPDs with reduced connector size and 286N for the e.max Press FPDs. All three IPS e.max ZirCAD groups statistically performed significantly better than IPS e.max Press (p<0.001). On the other hand, no significant difference could be established between the two IPS e.max ZirCAD MT3 groups with a 4mm×4mm connector size (p>0.05). The allowable maximum principal stress (σmax) which did not lead to failure during fatigue testing for IPS e.max ZirCAD MT3 was calculated between 208MPa and 223MPa for FPDs with 4mm×4mm connectors for 2×106 cycles. This value could also be verified for the FPDs of the same material with 3mm×4mm connectors. On the other hand fatigue strength in terms of σmax at 2×106 cycles of IPS e.max Press was calculated to be between 78 and 90MPa. SIGNIFICANCE: The fatigue resistance of the translucent zirconia 3-unit FPDs was about 60-70% higher than that of the lithium disilicate 3-unit FPDs, which may justify their use for molar replacements, provided that a minimal connector size of 4mm×4mm is observed. Even with a limited number of specimens (n=9) per group it was possible to statistically differentiate between the tested groups.

Using a chewing simulator for fatigue testing of metal ceramic crowns.

OBJECTIVE: Dynamic loading is a more important predictor for the clinical longevity of ceramic crowns than static loading. However, dynamic loading machines are costly and mostly have only one test station. The SD Mechatronik Chewing Simulator (formerly Willytec) may be a cost-effective alternative to evaluate the fatigue resistance of metal ceramic crowns. METHOD: Four metal ceramic materials were tested on lower first molar crowns: GC InitiaI, Creation (Willy Geller), IPS InLine (Ivoclar Vivadent) and the new low-fusion IPS Style Ceram (Ivoclar Vivadent). The ceramic material was manually layered on frames made of the nickel-chromium alloy 4all (Ivoclar Vivadent) by using a silicone mould. The crowns were adhesively luted to PMMA dies. Dynamic loading was carried out with a SD Mechatronik Chewing Simulator using additional bars with weights. A steel antagonist (Ø 4mm) with 40mm/s downward speed hit the disto-buccal cusp of the crown with minimal impulse while sliding for a distance of 0.7mm. The starting load was 250N. The forces at each load level had been verified with a 3D force sensor (Kistler). Four crowns per group and load were submitted to four decreasing load levels for 200,000 cycles with a resulting simulation frequency of 0.9Hz and simultaneous thermocycling (5°C/55°C) until all four crowns no longer showed chippings. Statistical analyses had been carried out using an exponential, a Weibull and a lognormal model. The fatigue resistance was defined as the maximal load for which one would observe less than 1% failure after 200,000 cycles. In addition to the fatigue testing of the molar crowns, simulations of finite element method (FEM) were conducted in order to investigate the influence of the mismatch of the thermal expansion coefficient (CTE) between the PMMA die and the molar crown on the fatigue resistance. RESULTS: The 3D-force measurements revealed that the summarised forces were very similar to the force of the dead weights that were put on the bars. The failure modes consisted of cracks and small and big chippings. Chi-square test and Gamma revealed no statistically significant differences between the four test materials in relation to the failure mode. At 250N all materials showed chippings within the ceramic or down to the metal frame, while at lower loads there were differences. The estimated fatigue resistance was 68N for GC Initial, 88N for Creation, 96N for IPS Style Ceram, and 105N for IPS InLine, when using a Weibull model and considering all possible events. Furthermore, FEM simulations revealed that the maximum values of the maximum principal stress were 90 MPa for the thermocycling and 225 MPa for the external load. CONCLUSION: The SD Mechatronik Chewing Simulator is an adequate and cost-effective tool to test layered PFM crowns for fatigue resistance. The test method and the chewing simulator can be used for ceramic on metal, ceramic on zirconia and monolithic ceramic materials.

Efficacy of several serological tests and antigens for diagnosis of bovine brucellosis in the presence of false-positive serological results due to Yersinia enterocolitica O:9.

Yersinia enterocolitica O:9 bears a smooth lipopolysaccharide (S-LPS) of Brucella sp. O-chain A+C/Y epitopic structure and is a cause of false-positive serological reactions (FPSR) in standard tests for cattle brucellosis. Brucella S-LPS, cross-reacting S-LPSs representing several O-chain epitope combinations, Brucella core lipid A epitopes (rough LPS), Brucella abortus S-LPS-derived polysaccharide, native hapten polysaccharide, rough LPS group 3 outer membrane protein complexes, recombinant BP26, and cytosolic proteins were tested in enzyme-linked immunosorbent assays (ELISA) and precipitation tests to detect cattle brucellosis (sensitivity) and to differentiate it from FPSR (specificity). No single serological test and antigen combination showed 100% sensitivity and specificity simultaneously. Immunoprecipitation tests with native hapten polysaccharide, counterimmunoelectrophoresis with cytosolic proteins, and a chaotropic ELISA with Brucella S-LPS were 100% specific but less sensitive than the Rose Bengal test, complement fixation, and indirect ELISA with Brucella S-LPSs and native hapten or S-LPS-derived polysaccharides. A competitive ELISA with Brucella S-LPS and M84 C/Y-specific monoclonal antibody was not 100% specific and was less sensitive than other tests. ELISA with Brucella suis bv. 2 S-LPS (deficient in C epitopes), Escherichia hermannii S-LPSs [lacking the contiguous alpha-(1-2)-linked perosamine residues characteristic of Y. enterocolitica S-LPS], BP26 recombinant protein, and Brucella cytosolic fractions did not provide adequate sensitivity/specificity ratios. Although no serological test and antigen combination fully resolved the diagnosis of bovine brucellosis in the presence of FPSR, some are simple and practical alternatives to the brucellin skin test currently recommended for differential diagnosis.

Characterization of Brucella abortus O-polysaccharide and core lipopolysaccharide mutants and demonstration that a complete core is required for rough vaccines to be efficient against Brucella abortus and Brucella ovis in the mouse model.

Brucella abortus rough lipopolysaccharide (LPS) mutants were obtained by transposon insertion into two wbk genes (wbkA [putative glycosyltransferase; formerly rfbU] and per [perosamine synthetase]), into manB (pmm [phosphomannomutase; formerly rfbK]), and into an unassigned gene. Consistent with gene-predicted roles, electrophoretic analysis, 2-keto-3-manno-D-octulosonate measurements, and immunoblots with monoclonal antibodies to O-polysaccharide, outer and inner core epitopes showed no O-polysaccharide expression and no LPS core defects in the wbk mutants. The rough LPS of manB mutant lacked the outer core epitope and the gene was designated manB(core) to distinguish it from the wbk manB(O-Ag). The fourth gene (provisionally designated wa**) coded for a putative glycosyltransferase involved in inner core synthesis, but the mutant kept the outer core epitope. Differences in phage and polymyxin sensitivity, exposure or expression of outer membrane protein, core and lipid A epitopes, and lipid A acylation demonstrated that small changes in LPS core caused significant differences in B. abortus outer membrane topology. In mice, the mutants showed different degrees of attenuation and induced antibodies to rough LPS and outer membrane proteins. Core-defective mutants and strain RB51 were ineffective vaccines against B. abortus in mice. The mutants per and wbkA induced protection but less than the standard smooth vaccine S19, and controls suggested that anti O-polysaccharide antibodies accounted largely for the difference. Whereas no core-defective mutant was effective against B. ovis, S19, RB51, and the wbkA and per mutants afforded similar levels of protection. These results suggest that rough Brucella vaccines should carry a complete core for maximal effectiveness.

Evolución del concepto 'Fisioterapia' en estudiantes de la diplomatura de Fisioterapia / Evolution of the concept 'Physiotherapy' among third year studentsof the diplomate course

Objetivos: el presente trabajo explora la evolución del concepto 'Fisioterapia' en alumnos de tercer curso de la diplomatura después de 3 años de instrucción. Muestra y método utilizado: al final de la diplomatura se aplicó a la muestra de alumnos del primer estudio (Serrado et al, 1997) las mismas pruebas que cuando estaban iniciando sus estudios (una de asociaciones libres y otra de definiciones). Resultados: los alumnos al terminar la carrera utilizan un vocabulario más técnico asociado a concepto 'Fisioterapia'; baja considerablemente la frecuencia de asociación con el término 'masaje' con relación al primer curso, y aumenta la corrección y especificidad de las técnicas nombradas. Las variaciones en la definición del concepto se refieren al aumento de la corrección, prevalecida de definiciones incompletas y al aumento de atribución de una finalidad 'preventiva' junto a la curativa. Los aspectos sociológicos ligados al concepto 'Fisioterapia' se mantienen primordialmente unidos al mismo cliché del primer curso: es 'arte y ciencia'. Conclusiones: al terminar la diplomatura, el concepto de 'Fisioterapia' en los alumnos se ha ampliado con respecto al primer estudio en lo que respecta a su finalidad preventiva/curativa. La ausencia de asociaciones con dimensiones sociales relevantes actualmente en esta profesión nos lleva a proponer que la formación de los/as fisioterapeutas debería tener en cuenta la integración de la educación sanitaria a las ciencias de la salud y la orientación hacia la comunidad, elementos que recientemente se han incorporado a las nuevas concepciones (y definiciones) de la Fisioterapia (AU)